Radiographic exposure control screen for the definition of detail of both hard and soft substance

ABSTRACT

The invention relates to a radiographic exposure control screen. It comprises a fluorescent layer and a visible light opaque layer, and is characterized in that the fluorescent layer diminishes penetrating rays selectively. The fluorescent layer has a low response value. Only the varied high intensity rays emanating from the thin object areas will cause fluorescence, and these strong rays will loose some of their intensity and energy in causing the fluorescence. The weakened rays will improve the definition of detail of thin object areas. It is well known in radiography, that relatively weak rays will define detail of soft substance. The weak rays emanating from dense object areas are not causing fluorescence, and therefore are not diminished by causing fluorescence, and will define the dense object areas. It can be seen that detail of both hard and soft substances will be defined in a radiograph.

United States Patent Georg S. Mittelstaedt 274 73rd St., Brooklyn, N.Y.11209 [2!] Appl. No. 804,931

[22] Filed Mar. 6, 1969 [45] Patented Apr. 20, 1971 [72] Inventor [54]RADIOGRAPIIIC EXPOSURE CONTROL SCREEN FOR THE DEFINITION OF DETAIL OFBOTH Primary ExaminerArchie R. Borchelt Assistant ExaminerDavis L.Willis ABSTRACT: The invention relates to a radiogra'phic exposurecontrol screen. It comprises a fluorescent layer and a visible lightopaque layer, and is characterized in that the fluorescent layerdiminishes penetrating rays selectively.

The fluorescent layer hasa low response value. Only the varied highintensity rays emanating from the thin object areas will causefluorescence, and these strong rays will loose some of their intensityand energy in causing the fluorescence. The weakened rays will improvethe definition of detail of thin object areas. It is well known inradiography, that relatively weak rays will define detail of softsubstance.

The weak rays emanating from dense object areas are not causingfluorescence, and therefore are not diminished by causing fluorescence,and will define the dense object areas.

It can be seen that detail of both hard and soft substances will bedefined in a radiograph.

PATENTEUAPRZOIQYI EEC-3.3

FIG. 6

FIG.5

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RAIIDIGGRAIPIIIIC IEXPUSIJRE CONTROL SCREEN FOR This invention primarilyrelates to radiography and photography and particularly relates to meansand methods to improve the definition of detail.

It is well known that is regular radiographs high intensities ofpenetrating radiation must be employed to define detail in hardsubstance e.g. bones, but then soft tissue e.g. flesh will beoverexposed and appear in a developed negative black or dark and vague,with little or no definition of detail.

Conversely, relatively low intensities of penetrating radiation willdefine detail in soft tissue, but then hard substance will beunderexposed and appear too light and vague, with little or nodefinition of detail.

According to the present invention, the simultaneous solution to both ofthese problems lies in the use between the object and a ray sensitivesurface of my ray-intensity control screen. In this screen, the highintensities of the ray image are selectively diminished, resulting inthe definition of detail in both dense and thin object areas.

The control screen as it will be called from here on, is a fluorescentscreen with a visible light opaque-penetrating ray transparent layer onthe ray exiting side, or on both sides, or enveloping the fluorescentscreen. The control screen is interposed between object and film orother light sensitive surface or area.

The control screen controls, that is, selectively diminishes the variedhigh intensities of penetrating radiation emanating from the object, toselectively lower the exposure of the relatively thin object areas.

In greater detail, the varied high intensity rays emanating from a thinobject area will produce varied fluorescence in the immediate controlscreen area through which they pass, the fluorescence consuming part ofthe ray energy in proportion to the degree or magnitude of fluorescence,thereby diminishing the high radiation intensities selectively. The nowweaker rays will define the density variations in the thin object areas.

The rays emanating from somewhat denser object areas will produce lessfluorescence in the control screen and therefore will be diminished to alesser degree, and the rays from very dense object areas-if anywillhardly cause any fluorescence in the control screen. Therefore the raysfrom these very dense object areas will hardly be diminished bycontrol-screen fluorescence.

It can be seen that the control screen will selectively diminish thehigher ray intensities emanating from the object. The varied intensitiesfrom relatively thin object areas will be selectively diminished, butthe low intensities from dense object areas will remain relativelyunchanged. The result is definition of detail in both dense and thinobject areas.

With the use of this control screen, the initial ray intensities can besomewhat higher than usual, to obtain improved definition of detail inhard substance. The interposed fluorescent control screen willautomatically and selectively diminish the excessive radiationintensities emanating from the soft tissues.

The main objects of this invention are to control the high radiationintensities emanating from thin object areas, and to improve thedefinition of detail.

These and other objects will become apparent in the description below,in which characters of reference refer to like-named parts in thedrawing.

The drawing is schematic and illustrates the principles of theinvention, but the invention and application is not limited to theparticular examples illustrated, nor to the particular constructionshown.

The features are shown in greatly enlarged form in the diagrammaticdrawing.

Referring briefly to the drawings:

FIG. 1 illustrates an embodiment of the invention showing a ray controlscreen comprising a fluorescent layer and an opaque layer on the rayexiting side of the fluorescent layer.

FIG. 2 shows a fluorescent layer and opaque layers on both sides of thefluorescent layer.

FIG. 3 shows a fluorescent layer and an opaque layer completelyenclosing the fluorescent layer.

FIG. 4 shows two fluorescent layers and an opaque layer between the twofluorescent layers.

FIG. 5 shows the ray intensity control screen of FIG. 1 disposed aheadof an image intensifier tube.

FIG. 6 is similar to FIG. 1, but it shows a separate support for thecontrol screen.

Referring in greater detail to the drawing, the numeral 1 in FIG. Iindicates a fluorescent layer, and the numeral 2 indicates a visiblelight opaque-penetrating radiation transparent layer on the ray exitingside of the fluorescent layer 1. The arrow (in this FIG. and in allother FIGS.) indicates the direction of the penetrating radiationemanating from an object. The fluorescence of the layer I will consumeray energy in proportion to the degree of fluorescence, and thereforewillv diminish the high intensities of the penetrating rays emanatingfrom the thin object areas in proportion to the magnitude offluorescence. The opaque layer 2 will confine the fluorescent light.Relatively weak rays from dense object areas will hardly causefluorescence and therefore will be relatively undiminishedTherefore,with the use of this control screen, both dense and thin object areaswill be defined.

The basic parts and features will be given the same numerals in allFIGS. as is practicable.

FIG. 2 shows a control screen with opaque layers on both sides of thefluorescent layer 1. The opaque layer 3 is shown on the ray enteringside of the fluorescent layer 1, and the opaque layer 2 is shown on theray exiting side of the fluorescent layer 1. Of course, the positionscould be reversed. It is important in this invention that all thefluorescent light generated in the control screen is confined in thescreen. This fluorescence is not to illuminate or for producingexposure; it is only to selectively diminish overly high rayintensities. In this device, the varying high radiation intensities fromrelatively thin object areas are diminished in the fluorescent layer Iof the control screen in proportion to the degree or magnitude offluorescence they cause. The opaque layers 2 and 3 will effectivelyconfine the fluorescence of the layer 1 within the control screen, andthe selectively diminished ray intensities will define the densityvariations in relatively thin object areas. The low ray intensitiesemanating from the dense object areas will cause little or no fluorescein the control screen. They will remain relatively undiminished and willdefine the dense object areas. Therefore both dense and thin objectareas will be defined. The arrow indicates the direction of penetratingrays emanating from the object.

FIG. 3 is similar to FIGS. 1 and 2, but here the opaque layer 2completely encloses the fluorescent layer 1, to fully confine thefluorescent light in the control screen. The arrow indicates thedirection of penetrating radiation emanating from the object.

FIG. 4 shows two fluorescent layers 1 and 4 and a visible lightopaque-penetrating ray transparent layer 2 between the two fluorescentlayers. The fluorescent layer I diminishes the penetrating rays from therelatively thin object areas in proportion to the degree of fluorescencethey cause, and the opaque layer 2 confines the fluorescence. Thefluorescent layer 4 is either an intensifying screen or a fluoroscopicscreen. Again, the arrow indicates the direction of penetratingradiation emanating from the object. The result of this arrangement isdefinition of detail in both dense and thin object areas.

FIG. 5 shows a control screen similar to that of FIG. I, showing afluorescent layer 1, and an opaque layer 2 on the ray exiting side ofthe fluorescent layer 1. Here, the control screen is placed immediatelyahead of an image intensifying tube 5 for electronic magnification. Thearrow indicates the direction of penetrating radiation emanating fromthe object. The fluorescent layer I will diminish the high intensityradiation emanating from thin object areas, and the opaque layer 2 willconfine the fluorescent light.

FIG. 6 shows a control screen similar to that of FIG. 1, but it shows asupport 6. The fluorescent layer 1 is disposed on the support 6, and theopaque layer 2 is disposed on the ray exiting side of the fluorescentlayer 1. The arrow indicates the direction of the penetrating raysemanating from an object.

The control screen may be used in combination with any ray sensitivesurface or device and may be disposed ahead of a sensitive photographicfilm, or of an intensifying screen, or fluoroscopic screen, or ahead ofan image intensifier tube, or ahead of any other light sensitive surfaceor device.

It is to be noted that the fluorescence of the control screen is onlyused to selectively diminish the penetrating rays emanating from therelatively thin object areas. This fluorescent light is not forillumination or exposure.

There must be a visible light opaque-penetrating ray transparent screenor layer at least on the ray exiting side of the fluorescent layer ofthe control screen, but for highest efficiency the opaque screen orlayer must be disposed on both sides of the fluorescent layer, or allaround the fluorescent layer, perhaps in the form of a covering orenvelope, to completely cover the fluorescent layer.

To be efficient, the opaque layer must be completely impervious to thevisible fluorescent light, but must be penetrating ray transparent. Theopaque layer may consist of light metal e.g. aluminum, light alloys,plastics, compounds, pigments e.g. lamp black, opaque cardboard, paperor paints, or may consist of any other opaque material.

The opaque layer may be a separate layer, or may be attached to or bepart of the fluorescent layer in the control screen. The opaque layermay also be part of a casette or of some other radiographic element ordevice used in combination with the control screen; or any other meansor method may be used to limit the visible fluorescent light of thecontrol screen.

The opaque layer may serve as support for the fluorescent control screenlayer or vice versa, or there may be a separate support.

The control screen is placed ahead of a light sensitive surface or areae.g. a sensitive photographic film, an intensifying screen, afluoroscopic screen or an electronic intensifier, but combinations canbe made, and this forms part of this invention.

For instance, a control screen-intensifying screen combination may bemade comprising two fluorescent layers and an opaque layer between thetwo fluorescent layers. The opaque layer may be a separate sheet or maybe attached to either fluorescent layer or to both layers. The frontfluorescent layer in combination with the opaque layer is a controlscreen, and the back fluorescent layer is an intensifying screen.

Likewise, a control screen-fluoroscopic screen combination may be madecomprising two fluorescent layers and an opaque layer between the twofluorescent layers. Here too, the opaque layer may be a separate sheetor may be attached to either fluorescent layer or to both. The frontfluorescent layer in combination with the opaque layer is a controlscreen, and the back fluorescent layer is a fluoroscopic screen.

Any other control screen-sensitive surface combination may be made. Thisincludes control screen-photographic film combinations, controlscreen-electronic intensifier combinations, or any other combinations.All this forms part of this invention.

It is important that the high intensities from thin object areas willcause effective fluorescence in the control screen. It is also importantthat the low intensities from dense object areas will not causeeffective fluorescence in the control screen. To that end, i usefluorescent material of a low order number in the fluorescent controlscreen layer, and/or I add efficiency-reducing impurities known aspoisons or killers to the fluorescent material. Iron and nickel, forinstance, are such efficiency reducing substances, and as little as0.0000l percent of iron or nickel poison discernible decreases theefficiency in pure zinc sulphide. I propose to use in my selectivecontrol screen (for normal use) up to 1 percent of iron or nickelpoison, or both, and if higher ray intensities are employed up toseveral percent or higher.

O ther killer or poison substances may be used.

Other examples of fluorescent crystals are calcium tungstate and cadmiumborate.

It can be seen that the high ray intensities from thin object areas willcause fluorescence in the control screen areas through which they pass,but the low ray intensities from dense object areas will not causenotable fluorescence in the control screen areas through which theypass. The high ray intensities from thin object areas will be diminishedby the fluorescence to define the density variations in thin objectareas, but the low intensities from dense object areas will not bediminished by fluorescence and therefore will define detail in the denseobject areas.

The control screen may be used ahead of any ray sensitive screen e.g. anintensifying screen; but instead of or in addition to using anintensifying screen, a photographic emulsion may be treated with afluorescent substance to transform the short wave lengths of thepenetrating rays into longer ones, for augmenting the exposure caused bythe penetrating rays. The ethyl carboxylic ester of dihydrocollodium forinstance is suited for this purpose.

Examples of penetrating rays are X-rays, alpha, beta, gamma rays etc.

This invention may also be used to improve the definition of detail inexposed and developed radiographic and photographic film. Here,penetrating rays are passed through the developed film, then through thedescribed control screen, and then to a ray sensitive surface. The imagemay then be further processed. The high intensity rays emanating fromthe light film areas are diminished in the fluorescent control screenlayer in proportion to the degree of fluorescence. This is important todefine the light film areas. The low intensity rays from dense and darkfilm areas will not produce any effective fluorescence and thereforewill not be diminished by fluorescence. This is important for thedefinition of detail in the dense and dark film areas. It is also to benoted that in this application of the invention, the densitydifferentiations invisible inherent in the dark film areas will bedefined in the resulting radiograph.

In the text and claims, by intensity is also meant energy or magnitudeof radiation; by opaque is meant visible fluorescent lightimpervious-penetrating ray transparent; by opaque layer is also meant anopaque screen, covering or envelope, or an opaque part of a casette orof some other radiographic element or device used in connection with thecontrol screen; by fluorescent" is also meant phosporescent; by visiblelight is also means visible fluorescent light; by film is also meantphotographic film; by object is also meant exposed and developedphotographic or radiographic film; by surface" is also meant area; bylayer is also meant sheet, screen and vice versa; by X-rays for normaluse is meant up to about K.V.

The principles involved in this invention may be applied to all fieldsof radiography and/or photography, and changes may be made withoutdeparting from the spirit or scope of the invention.

lclaim:

1. In a radiographic exposure control screen comprising a fluorescentlayer and an opaque layer limiting the fluorescent light, sufficientkiller substance in the fluorescent layer to prevent fluorescence underthe weak rays emanating from dense object areas.

2. In a radiographic exposure control screen comprising a fluorescentlayer and an opaque layer limiting the fluorescent light, low responsefluorescent material in the fluorescent layer responding only to thestrong rays emanating from relatively thin object areas, thefluorescence diminishing said strong rays in proportion to the degree offluorescence, resulting in improved definition of detail of the thinobject areas; the weak rays emanating from the dense object areas notcausing effective fluorescence and therefore being undiminished byfluorescence, resulting in definition of detail of the dense objectareas.

1. In a radiographic exposure control screen comprising a fluorescentlayer and an opaque layer limiting the fluorescent light, sufficientkiller substance in the fluorescent layer to prevent fluorescence underthe weak rays emanating from dense object areas.
 2. In a radiographicexposure control screen comprising a fluorescent layer and an opaquelayer limiting the fluorescent light, low response fluorescent materialin the fluorescent layer responding only to the strong rays emanatingfrom relatively thin object areas, the fluorescence diminishing saidstrong rays in proportion to the degree of fluorescence, resulting inimproved definition of detail of the thin object areas; the weak raysemanating from the dense object areas not causing effective fluorescenceand therefore being undiminished by fluorescence, resulting indefinition of detail of the dense object areas.